Many different techniques have been employed in the canning of fruit such as pineapple and peaches. For example, in the technique described in U.S. Pat. No. 1,782,761, pineapple is canned in the absence of syrup. The pineapple pieces first are saturated with warm syrup in an air-tight tank. Then, a high vacuum of about 29 inches is drawn in the tank for several minutes to remove air from the pieces. Thereafter, air is admitted into the tank and the atmospheric pressure drives the syrup into the voids of the pineapple pieces to saturate the same. Finally, the pieces are drained and sealed in cans which are then retorted at sterilizing temperatures.
An important deficiency of the above technique of processing pineapple is that drawing the high vacuum for the indicated time to drive out the air is an extremely expensive operation. Also, at the indicated pressure, the boiling point is substantially below sterilizing temperatures. Thus, it is not possible to raise the fruit temperature to a level sufficient for sterilization during treatment in the tank. Thus, it is necessary to sterilize the pineapple after canning. This is relatively expensive since the heat must be sufficient to raise the coldest portion of the fruit in the center of the can to sterilizing temperatures which requires heating the fruit to the outside of the can well above that temperature for a relatively long time. This prolonged cooking imparts an undesirable cooked taste or off-flavor to this outside fruit and causes the vitamin C content of the fruit to be substantially reduced. Furthermore, this heating step slows down the entire canning operation.
Conventional operations presently employed in the canning of fresh fruit include filling the fruit pieces in the cans prior to treatment with syrup. This requires that the fruit be sterilized within the cans, an inefficient operation for the reasons set forth above. Also, there is no ability to drain the syrup from the fruit prior to sealing the cans.